Broadband light sources are used for various applications in the semiconductor processing industry. These applications include wafer inspection systems and lithography systems. In both types of systems it is desirable for the light source to have a long useful lifetime, high brightness and a broad spectral range of emitted light. Currently plasma-based light sources are used in lithography and wafer inspection systems. Plasma-based light sources generally include an enclosure containing a cathode, an anode and a discharge gas, e.g., argon, xenon, or mercury vapor or some combination of these. A voltage between the cathode and anode maintains a plasma or electric arc.
Broadband light sources often find use in semiconductor wafer inspection tools and steppers. In such tools, light from the plasma or arc may be collected with an ellipsoidal mirror and focused into the end of a light pipe. In wafer inspection tools, defect detection is sensitive to the angle of incidence of light depending on the type of defect. It is desirable, therefore, for illumination from the light pipe to provide a proper range of incident angles. Sometimes the distribution of incident angles (referred to sometimes as the pupil fill) is non-uniform or less than ideal.
It is within this context that embodiments of the present invention arise.